Full-Field Geometric Imperfection Measurement Using A Projection Speckle Correlation Method And Computational Modeling Of Cold Formed Steel Rack Uprights

Abstract

Copyright © 2022 by The Hong Kong Institute of Steel Construction and The Author(s). The objective of this study is to provide an innovative and efficient method to measure the geometric imperfections of complex sections such as steel rack uprights and to numerically study their behavior with imperfection sensitivity. Steel rack uprights are generally thin-walled cold-formed steel members, and their compressive capacity and stability are sensitive to initial geometric imperfections. Due to the complexity of the section, accurately measuring the imperfection of such sections could be challenging and labor-intensive. In this paper, the projection speckle correlation method and close-range photogrammetry technique are used to measure the full circumference morphology of the steel rack upright and obtain a 3D point cloud morphology of the member specimen. The initial geometric imperfection is then calculated from the point cloud database. Some characteristics of the imperfection field in the member are further analyzed. The proposed measurement method in this paper, as the first of its kind in the application of geometric imperfection measurement for cold-formed steel structures, has the advantages of low cost, high-speed, and high precision in 3D full-field geometric imperfections for complex sections, and can help further develop more reliable imperfection models for simulations. Moreover, the shell finite element (FE) model is established from the point cloud database along with the ideal member of the upright. Geometric imperfections are also incorporated into the ideal model of the upright in the FE nonlinear collapse analysis to study imperfection sensitivity and compare with the point-cloud model. The results highlight the sensitivity in selecting the imperfection mode shape and its magnitude using the traditional modal approach, which warrants more imperfection databases for the upright.